1. Field of the Invention
This invention relates to a sheet metal drawing equipment, and more particularly to a sheet metal. drawing equipment which is adapted to carry out a sheet metal drawing operation while finely controlling application of force to a tip end of a bit welded to a sheet metal material.
2. Description of Related Art
A sheet metal drawing equipment which is adapted to draw any depression formed on a surface of a sheet metal material by means of a fixture or tool welded to the surface, to thereby smooth the surface has been conventionally known in the art. Such a conventional sheet metal drawing equipment of a first type is a slide hammer type which is generally constructed as shown in FIGS. 1 and 2. More particularly, the sheet metal drawing equipment includes a tool 500 to be welded to a surface 400 of a sheet metal material and a hook temporarily held on one end of the tool, so that the surface of the sheet metal is drawn by shock. Also, a conventional sheet metal drawing equipment of a second type is proposed in Japanese Utility Model Publication No. 27290/1987 (62-27290) by the same applicantas that of the present invention.
Further, a conventional sheet metal drawing equipment of a third type is proposed, which is constructed as shown in FIG. 3. More particularly, an equipment generally designated at reference numeral 800 is a slide hammer type which is fed with a weak current to weld a tip end of a bit to a surface of a sheet metal material. For this purpose, the equipment 800 is provided at a distal end thereof with a bit 825 which is kept welded to the surface during drawing. Also, the equipment 800 includes a grip section 810 provided therein with an electrode and a body section 820 having a slide hammer 821, which are connected to each other by means of a screw 830. The bit 825 is fed with an electric current, resulting in being welded to the surface of the sheet metal material. Then, the slide hammer 821 is slid to generate shock, so that a depression on the surface of the sheet metal material may be drawn.
Unfortunately, the equipment of the first type causes shock generated by the hook to separate the tool 500 kept welded to the surface 400 therefrom during drawing. Also, it carries out drawing while applying force due to the shock to the tool 500, so that the surface of the sheet metal material which has been drawn tends to be roughed. Further, in the first type, it is highly difficult to adjust force applied to the tool during drawing, to thereby cause excessive drawing. Moreover, it is substantially impossible to carry out drawing sufficient to smooth the surface of the sheet metal material in a short period of time.
The equipment of the second type is conveniently applied to rough drawing wherein force required for drawing is transmitted through a tool to a surface of a sheet metal material to draw the sheet metal material over a relatively large area at a stroke. However, it is not suitable for carrying out drawing while finely applying force to the tool as in fine drawing which is required after the rough drawing, drawing carried out on a small area, drawing carried out on a very specific place or the like.
In the equipment of the third type, the grip section 810 is kept fixedly connected to the body section 820 by means of the screw 830 during drawing. However, shock occurring due to operation of the hammer causes damage to the electrode, a failure of a switch means 811, looseness of connection between the grip section 810 and the body section 820 and the like, leading to a failure in satisfactory electrical contact. Also, connection between the grip section 810 and the body section 820 requires to use the screw, resulting in being highly troublesome. Furthermore, the equipment causes selection of a position and a direction which facilitate handling of the tool to be substantially restricted, because the grip section 810 and body section 820 are fixed to each other using the screw 830 and a cord 840 is arranged on the side of the grip section.